Multidisciplinary studies - including clinical, immunologic, pathologic, epidemiologic and molecular genetic investigations - are being used to complement findings in each area and overcome limitations inherent in each approach. Current studies are focusing on: exploring possible environmental risk and protective factors; identifying genetic risk and protective factors by candidate gene and whole genome SNP analyses; defining the associations among clinical, laboratory and immunologic features of autoimmune diseases for diagnostic, prognostic and pathogenic purposes; and understanding differences in epigenetics, gene expression and proteomic patterns between monozygotic twins discordant for disease. Evaluation of exposures to silica, organic solvents, ultraviolet light, vaccinations, selected drugs and dietary supplements, hormones and pregnancy, tobacco smoke, stressful life events and infectious agents in the development of systemic autoimmune diseases are being conducted via a study of twins and close siblings discordant for systemic autoimmune disease. Little is known about the prevalence, types, and sociodemographic and biobehavioral correlates of autoimmunity, and antinuclear antibodies (ANAs) are the best general test for autoimmunity. Therefore, we conducted a cross-sectional analysis of 4,754 individuals from the National Health and Nutrition Examination Survey 1999-2004. ANAs were assessed by indirect immunofluorescence. In ANA-positive individuals, cellular staining patterns were determined, and specific autoantibody reactivities were assessed by immunoprecipitation. We found that the ANA prevalence in the US population of individuals ages 12 years and older was 13.8% (95% confidence interval 95% CI 12.2-15.5%). Our findings suggest that more than 32 million persons in the US have ANAs, and that the prevalence is higher among females, older individuals, African Americans, and those with a normal body weight. These data will serve as a useful baseline for future investigations of predictors and changes in ANA prevalence over time One of the objectives of the NIH twin-sib study is to determine if multiple systemic autoimmune diseases (SAID) share gene expression pathways that could provide insights into pathogenic mechanisms common to these disorders. To assess this, RNA microarray analyses were used to quantify gene expression in peripheral blood cells from 20 monozygotic (MZ) twin pairs discordant for SAID. Six affected probands with systemic lupus erythematosus (SLE), six with rheumatoid arthritis (RA), eight with idiopathic inflammatory myopathies (IIM), and their same-gendered unaffected twins, were enrolled. Comparisons were made between discordant twin pairs and these were also each compared to 40 unrelated control subjects (matched 2:1 to each twin by age, gender and ethnicity) using statistical and molecular pathway analyses. Relative quantitative PCR was used to verify independently measures of differential gene expression assessed by microarray analysis. We found that probands and unrelated, matched controls differed significantly in gene expression for 104 probes corresponding to 92 identifiable genes. Differentially expressed genes involved several pathways including immune responses, signaling, transcription/translation regulators and metabolic functions. Interferon (IFN)-response genes were up-regulated in probands compared to unrelated controls. Many of the abnormally expressed genes played regulatory roles in multiple cellular pathways. In unaffected twins intermediate ordering was observed for 81% of the probes whose expression differed significantly between probands and unrelated controls. Thus, alterations in expression of a limited number of genes may influence the dysregulation of numerous, integrated immune response, cell signaling and regulatory pathways that are common to a number of SAID. Gene expression profiles in peripheral blood also suggest that for genes in these critical pathways, unaffected twins may be in a transitional or intermediate state of immune dysregulation between twins with SAID and unrelated controls, perhaps predisposing them to the development of SAID given the necessary and sufficient environmental exposures. A group of poorly-understood, life-threatening autoimmune muscle diseases called the myositis syndromes or idiopathic inflammatory myopathies (IIM) are defined by chronic muscle inflammation and weakness and are associated with specific autoantibodies. The major forms of myositis are polymyositis, in which multiple muscles are affected by inflammation, and dermatomyositis, in which patients also develop skin inflammation. Yet there appear to be other types of myositis based on the clinical presentations, pathology and autoantibodies. We are also studying children who develop myositis and we have recently assessed whether certain environmental factors temporally associated with the onset of juvenile idiopathic inflammatory myopathies (JIIM) differ between phenotypes. Physicians completed questionnaires regarding documented infections, medications, immunizations and an open-ended question about other noted exposures within 6 months before illness onset for 285 patients with JIIM. We found that 60% of JIIM patients had a reported exposure within 6 months before illness onset. Most patients (62%) had one recorded exposure, 26% had two and 12% had three to five exposures. Patients older than the median age at diagnosis, those with a longer delay to diagnosis and those with anti-signal recognition particle autoantibodies had a higher frequency of documented exposures. Infections were the most common exposure and represented 44% of the total number of reported exposures. Non-infectious exposures included medications (18%), immunizations (11%), stressful life events (11%) and unusual sun exposure (7%). Exposures varied by age at diagnosis, race, disease course and the presence of certain myositis autoantibodies. Thus, JIIM may be related to multiple exposures and these appear to vary among phenotypes.